Silo compartment for materials in powdery form



United States Patent 3,138,296 SlLt) COMPARTMENT FOR MATEREALS 1NPOl/VDERY FORM Karl Neidhardt, Qologne-Deutz, Germany, assignor toGebriider Biihler, Uzwil, Switzerland, a firm Filed Jan. 31, 1961, Ser.No. 86,209 Claims priority, application Germany Feb. 3, H60 1 Claim.(Cl. 222-185) This invention relates to a silo compartment for loose orbulk materials in powdery or dust form which only flow with difiiculty,advantageously flour, and especially to the design of a dischargesection of silo compartments for tall silos.

The discharge of the silo compartments for freely flowing bulkmaterials, for example, of coarse grain type, is generally formed bysimple sloping discharge devices, since obstruction due to caking or thelike scarcely occurs with such loose materials. The discharge of loosematerials in powdery or dust form from silo compartments frequentlypresents difiiculties, because first the material tends to cake togetherbecause of a natural humidity and secondly the procedure has recentlybeen adopted of employing silo compartments of considerable height, withwhich pressure causing strong compression of the material are set upbecause of the high silo filling.

Attempts have already been made to overcome these difliculties byvarious means, but it has not so far been possible to achieve asatisfactory solution. For example, oscillating rocker beams have beenarranged both longitudinally and transversely of the outletfrom thecompartment. Owing to the considerable height of the compartment whichcan reach 30 meters and higher, the pressure loading on such rockerbeams is so high that disturbances occur. A displeasing feature in thiscase is also that material can be deposited beneath the rocker beams andthis is undesirable on hygienic grounds where foodstulfs are concerned.Where sloping surfaces are arranged before the outlet of thecompartment, these are disposed with a comparatively steep inclination,which is scarcely below approximately 75. Silo compartments equippedwith stirrer devices are also not satisfactory. On account of thesloping surfaces, experience shows that they tend to set up disturbancesin the discharge because of bridge formation flour. Furthermore,so-called crossbottom silos exist, in which each half of the dischargeportion of the silo chamber is fitted with sloping surfaces which areinclined in diametrically opposed directions. In this case, on the onehand, the constructional costs are high due to the high base pressures,but on the other hand, with moist material, interruptions in the floware set up on the side opposite the opening, since the material canbecome wedged between the sloping surfaces, which are likewise inclinedat an angle of about 75. Consequently, silo compartments have also beenused which have walls which remain vertical as far as the discharge end,that is to say, are without sloping surfaces, and chain dischargedevices are arranged at the bottom of the silo compartment. However,these discharge chains are loaded by the pressure of all the contents ofthe compartment and they must be moved over the bottom under this load.The conveyor chains are consequently subjected to a comparatively highdegree of wear and in addiiton there are possibilities of undesireddeposition of material Within the chain casing.

In order to obviate the said difficulties, which are always recurring,discharge devices have also been developed by which the material iscarried away by means of compressed air, with the use of filter basesand the like.

Such installations require special base constructions with specialfilter plates, compressed air installations, air-tight lock chambers,air-compensating installations and the like. The cost involved for thedischarge device isconsiderable and in addition there is also the dangerthat, depending on the nature of the contents of the compartment, thepores of the filter plates become clogged in time, so that theefiiciency of the installation is considerably reduced.

The invention is concerned with a constructional form of a silocompartment discharge device, with which the disadvantages. set forth nolonger occur. It is characterized in that the discharge section of thesilo compartment comprises on the one hand a nose-like member projectinginto the compartment space on the compartment wall above the dischargeopeningand spaced from the end of the compartment and a slopingdischarge surface is provided on the opposite compartment wall at alower level, and on the other hand that compartment wall which isopposite the nose-like member merges below the level of the end of thenose and by means of a troughshaped transition into the sloping surfacedirected towards the discharge opening. The sloping surface should havean angle relatively to the horizontal which is smaller than The designof the lower part of the outlet of the compartment as a space madetrough-shaped on one side results in that a considerable widening of thedischarge space becomes possible because of the rounding of thetransition from the vertical compartment wall to the sloping dischargesurface and also in view of the fact that the discharge opening is keptsubstantially free from the load of the material disposed in thecompartment by the projecting nose. The wedge action which is producedimmediately before the outlet and which otherwise leads to cakingtogether of the fiourdike material is avoided. The widening effectresulting from the rounding permits the setting up of a strong thrustmovement coming from above and changing into the sloping surface,whereby the column of flour, even under the most unfavorable conditions,is thrust by its own weight into the discharge space, where it can thenflow out of the outlet in a loosened form. The combination of theprojecting nose on the one side and the rounding at the transition fromthe vertical wall to the sloping surface produces the desiredsatisfactory result. Contrary to the opinion formerly held and also tocurrent practice, this combination makes it possible for the first timeto use sloping discharge surfaces which have an angle far below 70. Onthe contrary, the more the angular position of the sloping surfaceapproaches 45, the better is the effect according to the invention,because the discharge space becomes larger as the angular positionbecomes smaller. The wedge effect of the sloping surface in relation tothe oppositely disposed vertical wall is smaller with decreasing angularpositions of the sloping surface than with a sloping surface at 70". Itthus becomes possible by means of the design according to the inventionto reach the extraordinary value of about 4050 for the sloping dischargesurface. Any suitable device, such as a discharge gate or .even aconveyor belt, can be used as discharge means, the said device onlyregulating the outlet quantity. When using a discharge gate, therotational movement of the latter is organically disposed in the streamof flowing material and the rotation thereof is assisted by this how.

One embodiment of the invention is shown by way of example in theaccompanying drawing, in which:

FIG. 1 is a vertical section through the discharge portion of a silocompartment constructed according to the invention, and

FIG. 2 is a cross-section on the line 2-2 of FIG. 1.

The silo compartment 1 of square or rectangular crosssection is formedby the longitudinal walls 2 and 3 and the transverse walls 4 and 5.Provided on one longitudinal wall, for example on the wall 2, is aprojecting nose 6 having a sloping surface 7 directed away from the wall2 and projecting into the compartment space. At the end and as indicatedat 8, this sloping surface, without any transition, abruptly extendsrearwardly again to the compartment wall 2. Opposite the sloping surface7, the compartment wall 3 extends vertically. Attached to the wall 3 isa sloping discharge surface 9, which extends as far as the outletopening or discharge 10. The outlet opening is thus situated beneath theprojecting nose 6 and is preferably kept somewhat smaller in its freewidth than the lower end of the projecting nose. Any suitable dischargemember can be arranged beneath the outlet opening, and advantageously arotatable discharge gate 11. The transition from the vertical wall 3 tothe sloping surface 9 is preferably smoothly rounded as at 12. Thisrounding advantageously has a radius which corresponds at least to halfthe width of the compartment. A vibratory wall section 13 can beprovided on the compartment wall 2 below the projecting nose 6 and thevibration can be initiated by means of a switch 14 mounted on the wall6.

Due to the projecting nose 6 with the sloping surface 7 being at apredetermined distance above the outlet opening 10, the effect isachieved that the load of the contents of the compartment is to asubstantial extent already taken up in the zone A. Since the verticalwall 3 in this zone A opposes the perpendicular pressure of the materialof less resistance than the nose 6 serving to relieve the pressure onthe space disposed beneath it, the material on the vertical Wall 3 ispressed downwardly owing to the pressure resulting from the weight. Dueto the pressure loading, the material slides from the roundedtransitional region 12 to the sloping discharge surface 9 in the zone B.When the compartment is full, a pressurefree zone C is formed below thenose 6, and this permits a corresponding loosening of the materialleaving zone A. As soon as there is any withdrawal, it is the materialfrom the zone D immediately above the outlet opening 10 which isextracted. The thrust force acting more strongly along the compartmentwall 3, 12 and 9 than on the opposite wall 2, 7 displaces the materialinto those parts of zones B and D which become free and thereby causesthe contents of the compartment to fiow.

The outlet opening 10 is freed from the load of the contents of thecompartment by being covered by the projecting nose 6. At the slopingdischarge surface 9, it is possible to operate with a substantiallysmaller slope than 75 namely, with a slope of 40".

If it should be desired to empty the zone D after a relatively longstorage time, for example, with moist material without the materialsliding down from the other zones, assistance for a short time with thevibratory plate 13 is sufficient. For this purpose, the diaphragm switchlocated at 14 is operated and switches on the vibratory plate 13 for afew seconds. The material immediately starts to flow, pressure is againapplied to the diaphragm switch and switches off the vibration. It isonly relatively seldom that this assistance is necessary and in practiceis only required when the compartments have stood for a relatively longtime with moist material under full pressure. For the actual dischargeoperation, no auxiliary means, for example in the form of conveyorchains, compressed air installations, stirrer mechanisms and the like,are required.

The sloping discharge surface 9 preferably starts substantially at theheight of the lower part of the projecting nose disposed on the oppositecompartment wall. The

smaller the inclination, the more advisable is it for the rounding to beprovided at the transition from the vertical wall to the slopingsurface. In the example illustrated, the radius of the rounding is aboutthree-quarters of the width of the compartment. The depth of theprojecting nose 6 can generally be one-third to one-quarter of thecorresponding compartment width.

The satisfactory discharging of the material can also be assisted by thesliding surfaces in the discharge portion of the silo compartment beingformed of a material which is porous and absorbent, at least on thesmooth upper surface, while being hard and of high strength. Thematerial is also to be free from grease and oil. In this way, it ispossible to prevent the formation on the sliding surface of a film ofcondensate which would result in the separate flour particles stickingto the said surface and thereby causing a settlement of the loosematerial. Due to the fact that the material has a certain porosity, italso has a certain absorbent capacity, so that any condensate which isformed can be taken up by the material itself. The material shouldmoreover have a low thermal conductivity. This circumstance alsocontributes to counteracting a formation of condensate.

The material of the sliding surfaces is preferably formed of a hard-woodplywood board with a high surface smoothness. Beechwood and especiallyred beech is extremely advantageous for this purpose. White beech isalso to be considered, as well as maple or all woods with the saidproperties.

A high surface smoothness can be produced on the materials according tothe invention, preferably by the following method: First, the surfacesare preferably saturated with hot water. As a result, all pressure zoneswhich have for example been formed with plywoods or other boards by thepressing are removed. The rough surfaces formed in this way arethoroughly dried. The roughness is then carefully rubbed off withextremely fine-and sharp abrasives, as far as possible without usingpressure and in the direction of the grain. This operation can berepeated until no roughness can be found after surface treatment withhot water. In this way, there are provided sliding surfaces having asmoothness which is fully maintained, even under the action of thehumidity of the bulk material.

It is not absolutely necessary to use naturally grown materials for thepurpose according to the invention. The sliding portion of the slopingdischarge surface can also be formed by sheets or boards produced fromsawdust, perhaps in combination with synthetic resin powder, bypressing. In this way, a porous and absorbent surface is obtained, whichcan be provided with a high surface smoothness.

What is claimed is:

In a silo for storing and gravity-discharging fluent, pulverulentmaterial, said silo including a pair of opposed, parallel vertical wallsconnected by transverse side walls and defining a rectangularcross-sectional storage area for the pulverulent material; theimprovement comprising means for maintaining free, gravity flow ofmaterial from said silo comprising a nose portion integral with andextending transversely of the inner surface of one of said verticalwalls and including a planar, surface extending inwardly and downwardlyat a shallow angle toward a lower portion of the silo and said othervertical wall and terminating in an abrupt, lateral shoulder extendingbeneath said nose portion at substantially a right angle to said onevertical wall, said one vertical wall terminating in a lower edgesubstantially in the plane of said one vertical wall, said othervertical wall extending parallel to said one Wall to a point near theheight of said abrupt lateral shoulder and merging into an arcuatecorner of a radius at least equal to one-half the distance between saidvertical walls, said arcuate corner merging into an angular, bottom wallextending in a plane less than =23 with respect to the horizontal andterminating in a free edge spaced from an substantially coplanar withthe lower edge of said one vertical wall and defining therewith betweenopposed transverse margins a downwardly opening discharge slot disposedbeneath a downward projection of said abrupt shoulder of said noseportion, and discharge means disposed transversely beneath saiddischarge slot and exteriorly thereof for aiding to move gravitydischarged pulverulent material away from said discharge seat.

References Cited in the file of this patent UNITED STATES PATENTS EhmkeOct.,4,- 1898 Marsa Apr. 15, 1919 Snyder May 26, 1925 Sloan June 14,1938 Prater Apr. 11, 1944 Smith Nov. 21, 1944 Dalmas Apr. 10, 1951Hurter May 27, 1952

